[17.0][IMP] partner_firstname: add is_address_readonly and is_individual for more UI customizable

[CRogos]

We are currently unhappy that invoice or shipping address has a firstname. Shipping addresses sometimes need an department name or other additional information, which are not person/individual like.

Therefore I would like to make the module more flexible and add an overloadable attribute is_individual, where you can control whether firstname should be visible or not. Modules could overload the _compute_contact_type method to do a different type definition of address types.

I also changed the visibility of the UI elements to is_individual and is_address_readonly instead of the address type.
The is_address_readonly we use to add another address type "contact_address" which is an individual, but also has an editiable address like address type "other". We use "other" for office addresses of a company and need to filter out these contacts for not adding these contacts to e.g. newsletters. Nevertheless we need the possibility to add individual addresses e.g. for people who are mostly working in the homeoffice and don't need their mails to the office.#

What do you think of these changes? Maybe also add this into an own module #1891 (my preferred solution), but than partner_firstname needs to derive from this module because the views overwrite readonly/visibility.